1. Field of the Invention
This invention relates to the formation by chemical vapor deposition of platinum and platinum-containing films, using source reagent solution compositions of platinum-containing source compounds and complexes.
2. Description of the Related Art
Ferroelectric thin films formed of oxide compositions such as strontium bismuth tantalate (SrBi.sub.2 Ta.sub.x O.sub.y) are potentially useful as capacitor materials for the fabrication of microelectronic devices such as dynamic random access memory (DRAM) devices.
Various means and methods for deposition formation of such ferroelectric films have come into use or otherwise been proposed in the art, including sol-gel, spray pyrolysis, aerosol and liquid delivery chemical vapor deposition (CVD) techniques. The CVD approach is particularly advantageous because it enables high aspect ratio features to be efficiently coated and conformal films to be deposited over non-planar surface topographies.
In the fabrication of DRAM (as well as FRAM) devices, platinum metal (Pt) often is utilized as an electrode for the device. It would be desirable to form the platinum films by CVD as well, to integrate the manufacturing steps efficiently.
The chemical vapor deposition of Pt films over small-scale, localized areas has been carried out successfully using various solid precursors, including for example tetrakis (trifluorophosphine) platinum, bis (.beta.-diketonate) platinum, (cyclopentadienyl) platinum trimethyl, and (alkylcyclopentadienyl) platinum trimethyl, and inducing deposition of the platinum over the localized area by focused ion beam, electron beam, or laser decomposition of the platinum precursor. This technique may be used for, e.g., formation of platinum interconnects, microsurgery to correct subsurface chip defects, or repair of x-ray masks, as described in Tao and Melngailis, U.S. Pat. No. 5,104,684, "Ion Beam Induced Deposition of Metals." In general, such precursor compounds have superior volatility characteristics, being readily volatilized by sublimation from the solid phase in conventional bubbler-based transport systems for subsequent chemical vapor deposition in the deposition reactor. In consequence, the use of such conventional bubbler-based transport systems for forming the vapor of these solid precursors for platinum has proven sufficiently advantageous in terms of the rate of transport of the platinum source vapor to the downstream CVD reactor, so that alternative delivery techniques have not been actively sought.
However, when it is desired to form larger area platinum films with continuous coverage of surfaces of various geometries, there are suggestions that mass transport of these platinum reagents to the deposition reactor may be inadequate. For example, as reported in "Chemical Vapor Deposition of Platinum, Palladium and Nickel," Alfred A. Zinn, et al., in The Chemistry of Metal CVD, edited by Toivo T. Kodas and Mark J. Hampden-Smith, VCH Verlagsgesellschaft mbH, Weinheim, Germany and VCH Publishers Inc., New York, p. 337, low growth rates of platinum were reported and attributed to "an inadequate supply of the precursor to the reactor."
Examples of prior art CVD-based platinum deposition process technology include the compositions and coating formation technology disclosed in U.S. Pat. No. 5,130,172 issued Jul. 14, 1992 to Robert F. Hicks, et al. and U.S. Pat. No. 5,403,620 issued Apr. 4, 1995 to Herbert D. Kraesz, et al., which teach to form a platinum coating on a substrate from organometallic compounds such as (trimethyl)(cyclopentadienyl)platinum in the presence of a reducing fluid such as hydrogen gas.
In general, the transport rate of source reagent vapor to the CVD reactor in CVD process systems has a substantial impact on the ease and economics of operating such systems, and a means and method which markedly increases such transport rate of the reagent source material to the CVD reactor represents a significant advance in the art of chemical vapor deposition.
It therefore is an object of the present invention to provide an improved composition, means, and method for delivery of platinum source material to the reactor of a chemical vapor deposition process system.
It is another object of the invention to provide an improved Pt CVD process, which provides faster film growth rates via liquid delivery and eliminates the deleterious effects of having hydrogen in contact with capacitor "oxides" at elevated temperatures (i.e., .gtoreq.500.degree. C.), when Pt electrodes or other Pt thin film structures are formed on oxide substrates, as hereinafter more fully disclosed.
Other objects, features and advantages of the present invention will be more fully apparent from the ensuing disclosure and appended claims.